Masonry cement composition and masonry construction

ABSTRACT

A masonry cement is prepared by dry mixing Portland cement, diatomaceous earth and a water-swellable colloidal clay, such as bentonite. Accordingly, the crushed limestone and other ingredients previously included in masonry cements for admixture with Portland cement can be completely eliminated and substituted by diatomaceous earth and water-swellable colloidal clay. In this manner, a combination of less than about 10% by weight of a combination of diatomaceous earth and colloidal clay replaces approximately 50% by weight crushed limestone and other ingredients from prior art masonry cement compositions while providing a masonry cement which meets ASTM specifications, particularly for air entrainment, water retention and compressive strength.

BACKGROUND OF THE INVENTION AND PRIOR ART

In accordance with ASTM definitions, masonry cement is defined as a hydraulic cement for use in mortars for masonry construction, containing one or more of the following materials: Portland cement, Portland blast-furnace slag cement, Portland-pozzolan cement, natural cement, slag cement, or hydraulic lime; and in addition usually containing one or more materials such as hydrated lime, limestone, chalk, calcareous shell, talc, slag, or clay, as prepared for this purpose. The present physical requirements for type-S mortars to meet ASTM C91 specifications are as follows:

Compressive strength (average of 3 cubes): The compressive strength of mortar cubes, composed of 1 part cement and 3 parts graded standard sand by volume, prepared and tested in accordance with this specification shall be equal to or higher than the values specified for the ages indicated below:

    ______________________________________                                                 7 days, psi                                                                           500                                                                    (MPa)   (3.45)                                                                 28 days, psi                                                                           900                                                                    (MPa)   (6.21)                                                          ______________________________________                                    

Air content of mortar, prepared and tested in accordance with requirements of this specification:

    ______________________________________                                         Max. volume         22%                                                        Min. volume         12%                                                        Water retention, flow after                                                                        70%                                                        suction, of original flow                                                      ______________________________________                                    

To achieve these test results, mortars are prepared from the masonry cement of the present invention by proportioning the masonry cement to contain 188 pounds of cement, 50 pounds of high grade limestone and 720 pounds of sand. The sand shall consist of 80 pounds of graded standard sand ASTM C-91. The quantity of water, measured in milliliters shall be such as to produce a flow of 110±5 as determined by the ASTM flow table.

A typical prior art masonry cement contains approximately 188 pounds of Portland cement, 50 pounds high grade limestone and other components, such as an air entraining agent. Typically, masonry cements are manufactured by using a steel ball grinder to grind the limestone with the other components for admixture with the Portland cement. These prior art masonry cements require a relatively high percentage of limestone as a plasticizer to meet ASTM specifications for masonry cements. ASTM specifications for air content in a masonry cement provide for a maximum of 18% by volume to provide void spaces in the masonry cement for expansion of freezing moisture.

The use of a substantial quantity of limestone as a plasticizer in prior art masonry cements creates two significant problems. First, the substantial quantities of limestone necessary to provide sufficient plasticity to the masonry cement reduces the compressive strength of the cement. Second, the limestone must be crushed in a grinder together with other components, such as a polyglycol as a grinding aid, fatty acids as an air entraining agent, and a sucrose solution as a setting agent, to provide a slurry for admixture with the Portland cement. The grinder must be carefully cleaned after each batch so that the masonry cement can be manufactured as a consistent, precise composition. Further, if the masonry cement composition is to be changed between batches, the grinder must be completely cleaned after each batch to make sure that the masonry cement being manufactured meets the ASTM specification for the particular type of masonry cement since it may be prohibitive for a particular type of masonry cement to include a component of the masonry cement previously included in the last limestone grinding batch.

Others have used diatomite, diatomaceous earth, bentonite or hydrous silicates of alumina as a thickening agent in a concrete or mortar generally in an amount of about 2% by weight or less of the cement composition, as disclosed particularly in the Cross Pat. Nos. 1,854,180 and 1,943,584 and, additionally as disclosed in the following U.S. patents:

    ______________________________________                                         1,584,579      2,356,214    2,585,366                                          1,795,011      2,377,491    3,219,112                                          1,885,731      2,516,342                                                       1,920,358      2,529,841                                                       ______________________________________                                    

Bentonite and diatomaceous earth when added to Portland cement alone, as disclosed in the Cross Pat. Nos. 1,854,180 and 1,943,584, are not sufficient to provide the necessary water retention and air entrainment properties to make the cement useful as a masonry cement. Mortars prepared with Portland cement containing 2% and 4% by weight bentonite and mortars prepared with Portland cement containing 2% and 4% by weight diatomaceous earth were found to have the following values for water retention, insufficient to meet ASTM specifications.

    ______________________________________                                                                  Portland  Portland                                                             plus 2%   plus 4%                                            Portland                                                                               Portland  diato-    diato-                                             plus 2% plus 4%   maceous   maceous                                            bentonite                                                                              bentonite earth     earth                                       ______________________________________                                         Water    52        54        48      50                                        Retention                                                                      (min. 75%)                                                                     Air Content                                                                             11.9      10.7      7.4     6.8                                       (min. 12%)                                                                     ______________________________________                                    

Further, the Weber U.S. Pat. No. 2,643,193 discloses an insulating filler composition useful as an aggregate in place of sand for mixture with hard-wall plaster or cement adapted for mixture with Portland cement and containing both diatomaceous earth and colloidal clay. The maximum clay content, however, is less than 4% by weight and the composition is not adapted to be used as a masonry cement since the composition does not meet ASTM specifications.

This assignee's U.S. Pat. No. 4,377,416 discloses a mortar or masonry cement composition containing at least 5% by weight colloidal clay. In accordance with the present invention, it has been found that new and unexpected results are achieved in a mortar cement including Portland cement, about 0.05 to about 0.8% by weight diatomaceous earth; and about 0.5% to 4.0% water-swellable colloidal clay, such as bentonite. Surprisingly, when a masonry cement composition is prepared to contain, for example, 188 pounds of Portland cement, 720 pounds of graded standard sand and about 0.5% to about 4.0% bentonite based on the weight of Portland cement, diatomaceous earth and bentonite clay, thereby replacing the 50 pounds of limestone, the compressive strengths meet ASTM specifications and are about equivalent to the compressive strengths of masonry cements containing 20% to 42% limestone.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has been found that the crushed limestone and other ingredients previously included in masonry cements for admixture with Portland cement, sand and water can be completely eliminated and substituted by diatomaceous earth and one or more water swellable colloidal clays, such as bentonite. Accordingly, the masonry cement of the present invention includes Portland cement, diatomaceous earth and water swellable colloidal clay. In this manner, a combination of less than about 5% by weight of a combination of diatomaceous earth and colloidal clay, such as bentonite, replaces approximately 20% to 50% by weight crushed limestone and other ingredients from prior art masonry cement compositions while providing a masonry cement which meets ASTM C91 specifications for air entrainment, water retention and surprisingly, for compressive strength.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One of the ASTM requirements for masonry cements is that the masonry cement develop an initial set in a minimum of one and one half hours. Because of this initial set requirement, all mortars being used today begin to stiffen within a period of 15 to 25 minutes requiring the mortar to be "shaken" or re-tempered every 15 to 25 minutes, depending upon temperature and humidity conditions. The mortar is re-tempered by adding water to the mortar on the mortar board and stirring to homogeneously mix the water into the mortar so that the mortar again is a proper consistency and has a useable flow.

In accordance with an important and surprising feature of the present invention, the mortar composition of the present invention can be used without re-tempering for two to three times longer than prior art masonry cements. Although the need for re-tempering is substantially reduced, the mortar of the present invention will develop its initial and final set within the time limits of current ASTM specifications.

In accordance with another important, new and unexpected feature of the present invention, a 50 pound bag of the masonry cement composition of the present invention can be mixed with the same quantity of mason's sand meeting ASTM specification C-144, as a 70 pound bag of a typical prior art masonry cement containing approximately 45% high grade limestone and approximately 8% of other components, as previously described. It is very desirable for a mason or a mortar tender to be able to pour 50 pound bags instead of 70 pound bags to obtain substantially the same quantity of masonry cement, particularly where the masonry cement of the present invention does not require re-tempering for at least one hour.

A typical prior art bag of masonry cement weighs 70 pounds and includes approximately 35 pounds of Portland cement, approximately 29 pounds of high grade crushed limestone, 1.5 pounds of a polyglycol, 1.5 pounds of fatty acids, 1.5 pounds of an air entraining agent and 1.5 pounds of a sucrose solution. A typical masonry cement of the present invention weighs 50 pounds and contains about 48.75 pounds of Portland cement, type I, 0.25 pound of diatomaceous earth and 1.0 pound of bentonite.

The colloidal clay utilized in the present invention is one which will hydrate in the presence of water, i.e., will swell in the presence of water. In accordance with one important embodiment of the present invention, the colloidal clay is bentonite. A preferred bentonite is sodium bentonite which is basically a hydratable montmorillonite clay of the type generally found in the Black Hills region of South Dakota and in Wyoming. This clay has sodium as its predominant exchange ion. However, the bentonite utilized in accordance with this embodiment of the present invention may also contain other cations such as magnesium and iron. The replaceable or exchangeable cations may either be sodium or calcium. There are cases wherein a montmorillonite predominant in calcium ions can be converted to a high swelling sodium variety through a well-known process called "peptizing" The colloidal clay utilized in this invention may be one or more peptized bentonites. The colloidal clay utilized in accordance with the present invention may be any member of the dioctahedral or triocatahedral smectite group or mixtures thereof. Examples are Beidellite, Nontronite, Hectorite and Saponite. The colloidal clay, i.e., bentonite, generally is finely divided as known for use in water barrier panels and the like. Although any water hydratable colloidal clay can be used in this invention, it is preferred to mix two or more bentonties having different but complementary properties. It is known that mined bentonites, while all having generally the same chemical formula, can include various adsorbed surface ions or intermolecular ionic impurities which cause bentonties to have slightly different properties. For example, some bentonites have better tolerance to calcium ions than other bentonties while some bentonites have better plasticity or better polymer response. Accordingly, two or more bentonites, for example one bentonite known for its good plasticity, and one known for its calcium tolerance can be blended together before addition to the Portland cement component to achieve a mortar having excellent plasticity and calcium tolerance. In addition to providing for consistent mortar plasticizing performance, blending of bentonites having different properties improves properties such as resistance to calcium ion contamination and stability in the presence of low pH. Such properties are desirable in a masonry cement, since the Portland cement component can produce a high calcium environment, increasing the potential for exchange of sodium ions for calcium ions, the exchange affecting the hydration properties of the bentonite and consequently plasticity of the masonry cement. Hydration stability in the presence of lower than normal pH is very desirable since the water used in preparing masonry cement mortars is often brackish and of lower than normal pH.

The diatomaceous earth component used in accordance with the present invention can be of any type generally available. The diatomaceous earth should be ground to provide a relatively small particle size to increase the surface area. To achieve the full advantage of the present invention the dry particle size of the diatomaceous earth should be reduced to the extent that the surface area, as determined by BET Nitrogen adsorption, is at least 20 square meters per gram. It is preferred that the diatomaceous earth have surface area of at least 40 square meters per gram. As an example of a particular diatomaceous earth used in the masonry cement of the present invention, the diatomaceous earth has a surface area of 60 square meters per gram corresponding to the following gradiations:

    ______________________________________                                         Size Of The Particles                                                                            Maximum %                                                    ______________________________________                                         Greater than 20 microns                                                                          20%                                                          10 to 20 microns  20%                                                          1 to 10 microns   20%                                                          Less than 1 micron                                                                               40%                                                          ______________________________________                                    

In accordance with an important feature of the present invention, the masonry cement of the present invention includes Portland cement combined with 0.05% to 0.8% by weight diatomaceous earth and about 0.5% to 4.0%, preferably about 1.0 to 3.0% by weight water hydratable colloidal clay. The Portland cement, therefore, is generally included in the composition of the present invention in an amount in the range of about 95.2% to about 99.45% by weight. The amount of Portland cement can be reduced to as low as about 80% by weight to accommodate inclusion of other components such as Portland blast-furnace slag cement, Portland-pozzolan cement, natural cement, slag cement, hydraulic lime, limestone, chalk, calcareous shell, talc, slag, clay and/or additional water soluble polymers and water soluble dispersing agents to increase the colloidal clay viscosity, and plasticity such as disclosed in this assignee's prior U.S. Pat. No. 3,949,560, which patent is hereby incorporated by reference, in amounts of about 0-15% by weight. In every case, the final mixture must meet ASTM standards for masonry cements, as previously defined.

It should be noted for the purpose of this description of the present invention that the percentages described are for the masonry cement which does not include sand or water. The percentages are substantially changed when sand and water are added to make a mortar, but the additions of sand and water are made in accordance with ASTM specifications in standard amounts as with present prior art masonry cements and, therefore, applicant attaches no criticality to the water and sand additions needed to form a mortar. Accordingly, percentages are described for the masonry cement only.

In accordance with an important feature of the present invention, no wet grinding is necessary to manufacture the masonry cement of the present invention. All components of the masonry cement of the present invention are added to a blender and dry blended together thereby eliminating the time consuming and necessary wet grinding associated with the addition of limestone to prior art masonry cements.

Four masonry cement compositions were prepared in accordance with the present invention having varying percentages of Portland cement, diatomaceous earth, and bentonite, each composition being mixed with 3 cubic feet of silica sand and water and data were collected for flow, air content, water retention value and compressive strength in accordance with ASTM test procedures C-91. The following results were obtained as shown in examples 1-4:

EXAMPLE NO. 1

Mix Proportions: 48.75 lbs. Type I Portland Cement; 0.25 lbs. diatomaceous earth; 1.0 lb bentonite.

    ______________________________________                                         Flow               110                                                         Air Content        15                                                          Water Retention Value                                                                             85                                                          Compressive Strength                                                           7 Days             28 Days                                                     ______________________________________                                    

In addition, a typical presently available masonry cement, as obtained from Texas Industries, masonry cement includes three cubic feet of silica sand and water, and the following data were collected as shown in Example 2:

EXAMPLE NO. 2 (Prior art)

Mix Proportions: Texas Industries Masonry Cement: 35 lbs. (50.0% by weight) Type I Portland cement; 29.4 lbs (42 % by weight) high grade crushed limestone; 1.4 lbs (2% by weight) polyglycol; 1.4 lbs (2% by weight) fatty acids; 1.4 lbs (2% by weight) air entraining agent; 1.4 lbs (2% by weight) sucrose solution.

    ______________________________________                                         Flow               112                                                         Air Content        15.7%                                                       Water Retention Value                                                                              86                                                         Compressive Strength:                                                                         7 Days   28 Days                                                                950 PSI 1405 PSI                                                               985 PSI 1475 PSI                                                              1005 PSI 1390 PSI                                               Avg.:           980 PSI 1423 PSI                                               ______________________________________                                    

The prior art masonry cement composition of Example 2 requires re-tempering after each approximately 20 minutes at an 80° F. temperature. The masonry cement of Example 1, prepared in accordance with the present invention, under the same ambient conditions, does not require re-tempering for one to one and one half hours. Further, the cement of Example 1 pours better than the masonry cement of Example 2, has a better texture and does not appear to be as sandy as the masonry cement of Example 2. In terms of texture, when the masonry cement of Example 1 is "jointed out" with a mason's jointer, the masonry cement of Example 1 gives a much better, slicker finish and a more clean line to a wall than does the masonry cement of Example 2.

Although the present invention has been described by reference to only a single embodiment thereof, it will be apparent that numerous other modifications and embodiments may be devised by those skilled in the art and it is intended by the appended claims to cover all modifications and embodiments which fall within the true spirit and scope of the present invention. 

I claim:
 1. A dry, blended masonry cement composition consisting essentially of Portland cement, about 0.05% to about 0.8% by weight diatomaceous earth and about 0.5% to about 4.0% by weight colloidal clay.
 2. The masonry cement of claim 1 wherein said Portland cement is in an amount of at least 80% by weight of the entire composition.
 3. The masonry cement of claim 2 wherein said Portland cement is in an amount of about 95.0% to about 99.5% by weight.
 4. The masonry cement of claim 1 wherein said colloidal clay is bentonite.
 5. The masonry cement of claim 4 wherein said diatomaceous earth has a surface area of at least 20 square meters per gram.
 6. A dry, blended masonry cement composition consisting essentially of 75-99% by weight Portland cement; 0.05-0.8% by weight diatomaceous earth and 0.5-4.0% by weight water-swellable colloidal clay.
 7. The masonry cement of claim 6 wherein said colloidal clay is bentonite.
 8. Masonry construction comprising a plurality of discrete masonry building materials secured together with a layer of mortar, said mortar including sand, water and a masonry cement composition, said masonry cement composition consisting essentially of Portland cement, about 0.05% to about 0.8% by weight diatomaceous earth and about 0.5% to about 4.0% by weight of a water swellable colloidal clay, said percentages based upon the total weight of Portland cement, diatomaceous earth, and colloidal clay.
 9. The masonry construction of claim 8 wherein said masonry cement is Portland cement in an amount of at least 80% by total weight of portland cement, diatomaceous earth and colloidal clay.
 10. The masonry construction of claim 8 wherein the sand is in an amount of at least 2 cubic feet per fifty pounds of Portland cement, diatomaceous earth and colloidal clay.
 11. The masonry construction of claim 8 wherein said Portland cement of said masonry cement is in an amount of about 95.2% to about 99.5% by weight of Portland cement, diatomaceous earth and colloidal clay.
 12. The masonry construction of claim 8 wherein said mortar consists essentially of sand, 80%-99.5% by weight Portland cement; 0.05%-0.8% by weight diatomaceous earth; and 0.5%-4.0% by weight colloidal clay, said percentages based upon the total weight of Portland cement, diatomaceous earth and colloidal clay.
 13. The masonry construction of claim 8 wherein said colloidal clay is bentonite.
 14. The masonry construction of claim 13 wherein said diatomaceous earth has a surface area of at least 20 square meters per gram.
 15. The masonry construction of claim 13 wherein said diatomaceous earth has a surface area of at least 40 square meters per gram. 